What's the hottest mega-cap stock on the market right now? Palantir Technologies (PLTR 6.56%). Shares of the artificial intelligence (AI)-powered software provider have skyrocketed more than 70% year to date. No other stock with a market cap of at least $200 billion has delivered anywhere close to that gain. While many investors have hopped aboard the Palantir bandwagon, Warren Buffett isn't one of them. Don't expect the multi-billionaire to become a fan of the stock anytime soon, either. Here are three rea ...